This invention relates generally to materials separating apparatus for segregating electrically conductive metals from commingled materials and, in a further embodiment, for additionally segregating magnetic items from the commingled materials.
In copending U.S. patent application Ser. No. 552,576, now U.S. Pat. No. 4,003,850, filed Feb. 24, 1975, and assigned to the same assignee as the present invention, there has been disclosed a materials separator in the form of an inclined ramp having on its upper surface steady-state magnetic means for establishing an alternating series of oppositely directed magnetic fields. Commingled materials are directed in a stream onto the ramp and slide down sequentially through the static series of oppositely directed magnetic fields. Consequently, eddy currents are induced in the electrically conductive items, which eddy currents cooperate with the magnetic fields to exert uniformly directed forces on the conductors. Such forces have a decelerating component directed oppositely to the flow direction of the stream and an orthogonally directed component which draws the conductors laterally out of the stream. The extents of such lateral deflections of the conductors thus provide means for sorting the conductive materials while separating them from nonconductive materials in the stream which slide down the ramp normally undeflected.
Such a ramp-type separator performs quite satisfactorily for useful separation of commingled materials such as are found in municipal solid waste, for example, but may be undesirable in applications where the physical properties of two or more commingled materials are too similar to allow them to be efficiently segregated, or where the particle size of the materials is so small that a sufficiently large deflection cannnot be obtained on the ramp.
It has been established that for a conductive particle sliding on an inclined magnetic ramp, the lateral deflection is proportional to 3/2 power of the ramp length. Thus, in some applications the ramp must be of undesirable length.
The separator described in application Ser. No. 552,576 now U.S. Pat. No. 4,003,850 also has the disadvantage of being very sensitive to magnetic particles in the feed stream. Such particles will adhere to the ramp surface and will therefore degrade the performance of the separator.